[ARM] S3C24XX: GPIO: Start removal of S3C24XX_GPIO_BASE

The S3C24XX_GPIO_BASE makes it difficult to compress the
GPIO number space, and is only used in a few places of
which everything outside arch/arm/plat-s3c24xx/gpiolib.c
will be removed as soon as possible.

Change gpiolib.c to use the S3C2410_GPxCON register addresses
as the base for each bank, thus eliminating S3C24XX_GPIO_BASE.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>